The invention relates to a fire sensing method and a fire sensor apparatus that judges the existence of a fire by sensing gas produced at the time of the fire.
With conventional fire sensing methods and fire sensor apparatuses, it is a basic idea that the existence of a fire is judged by detecting one or more of the various products of the fire, such as smoke, heat or gas caused by fire, and that upon such detection a fire alarm will be generated. Conventionally proposed combination fire sensors involve various sensors, such as a CO gas sensor, a humidity sensor, and a temperature sensor. The more complicated sensors are designed to infer the level of danger in fires and gas leakages by applying fuzzy inference. However, where non-gas criteria are used, unacceptable delays occur in detecting the existence of a fire.
Even where the fire is detected by sensing a gas such as CO.sub.2 gas and CO gas, both of which are produced in the combustion process, the detection is made by comparing the gas density with a predetermined threshold level. However, such conventional fire sensors are designed to detect CO.sub.2 gas or CO gas produced in the combustion process after ignition. Typically, when the CO.sub.2 or CO level reaches a threshold that results in the existence of a fire to be judged, the fire has already grown intense and flames have become widely spread. Accordingly, the conventional sensor has the dangerous problem that the identification of the existence and location of a fire will be delayed.
Further, the mere improvement in fire detection sensitivity to achieve early location of fires creates the problem of erroneous alarms. For highly sensitive devices, increases in CO.sub.2 gas due to cigarette smoke or a like non-fire phenomenon cannot be distinguished from increases in CO.sub.2 gas due to a fire.